102" Whip Portable Base Antenna Set Up

[Rick330man]

I've got this little tri-pod mount with a 3/8" stud. On went a 102" Radio Shack stainless steel whip with a 6" stainless steel spring. For a counter poise, I used two 106" long pieces of copper wire. The SWRs were too high initially - higher on 40 and lower on 1 - so I took off the spring. Now, I'm at 1.98 on 40 and 1.64 on 1. Not great, but usable. This whole contraption is sitting on a table about 3 1/2 feet off of the ground.

There hasn't been much skip lately, so I was surprised to hear multiple Puerto Rico stations booming in. No other skip could be heard. There wasn't much local traffic at all.

I'll hook up again tomorrow to see what this can do.

 

[Marconi]

Rick I think a 1/4 wave ground plane so close to the Earth probably needs the radiator to be closer to 108" inches for CB. It might even work a bit better if the radials are also 108" inches...being this low. A model can show a little bit of what might be going on with your setup.

How high is the antenna feed point off of the ground?

Can you post a close up picture of your antenna?

If so, I can make a couple of models for this idea at channels 1, 20, 40, using the height you specify to the feed point.

 

[codeman]

I've have a 102" antenna mounted on a painter's pole that I can raise and lower due to my hoa situation. I can only get my swrs down to about a 1.80 or so. It works fairly well for me, I can make local contacts on sideband up to 60 miles away if they have a beam pointed towards me. There hasn't been too much skip here lately but I have made a few dx contacts so far. I was thinking of trying a spring on mine to see how it changes my readings.

 

[Marconi]

codeman, I didn't mean to suggest to Rick that his mismatch was a problem. The SWR match was all that he presented as being a concern. Rick may be much lower than you and that too will have some effect. You both seem to be reporting somewhat similar matching results.

Does your antenna have horizontal radials?

How high is your antenna to the feed point, and can you describe your setup with a little more detail?

Rick reported his antenna worked well in the situations he noted and that sounds like pretty good results to me. He also said he removed his 6" spring, so I took that to mean he was trying to improve the match or maybe balance the match a little better towards the middle of the CB band.

IMO, I believe this 1/4 wave antenna is a much better antenna when mounted up high. Better than most folks are willing to even consider.

The PDF file attached below shows the top section for my Marconi 4x, 1/4 wave base station ground plane. I attach this to the top of a 36' or 45' foot push-up pole and it works nicely with a very low SWR across a large bandwidth. It uses 4 x 102" ss whips, a mobile L bracket, and the radial hub for an A99. I have holes drilled for horizontal and slanted down radials.

Good luck to you both and keep us posted.

 

[M0GVZ]

At 3.5ft off the ground the proximity of the ground will be detuning the radials anyway.

The feedpoint impedance of a 1/4 wave vertical over a perfect ground is 36 Ohms so you wouldn't get a 1:1 SWR, more like a 1.5:1.

As your ground improves you find that the vertical element needs to be shorter. That means that if you're using a mobile CB antenna with a good ground plane you're going to be getting the Dremel out and cutting a few inches off it as there won't be sufficient adjustment in it. The SWR on your setup being 1.98 on 40m and being 1.64 on Ch1 shows it needs shortening more.

 

[Rick330man]

Twelve hours after I posted, the skip was rolling in. I picked up stations from Puerto Rico, all up and down the east coast, and the Gulf Coast as far west as Texas. The bigger surprise was all of the rare, in-state Florida skip: Pensacola, Panama City and Tallahassee.

The idea was to set up an easy-to-assemble temporary rig that I could set up anywhere: whether I'm in the back or on my boat anchored off an island down here. My regular base antenna had a short somewhere and I couldn't get up on the roof to take it down, so I set this little thing up just for kicks. Obviously, getting it up higher would be beneficial. I'll be tweaking this a little more so I can improve performance via adding height.

One thing I am disappointed in is the poor quality of the 102" Radio Shack stainless steel whip. I have a stack of them. They are rusting badly. In this environment, the use of poor quality alloy gets exposed real fast.

I'll keep noodling.

 

[Rick330man]

Rick I think a 1/4 wave ground plane so close to the Earth probably needs the radiator to be closer to 108" inches for CB. It might even work a bit better if the radials are also 108" inches...being this low. A model can show a little bit of what might be going on with your setup.

How high is the antenna feed point off of the ground?

Can you post a close up picture of your antenna?

If so, I can make a couple of models for this idea at channels 1, 20, 40, using the height you specify to the feed point.

No picture, but the feed point is 40" off the ground. The 2 counterpoise radials/wires are at 50 degree angles and they are 180 degrees opposite each other.